Abstract :
[en] Feasibility studies for deep geological radioactive waste disposal facilities have led
to an increased interest in the geomechanical modelling of its host rock. In France,
a potential host rock is the Callovo-Oxfordian claystone. The low permeability
of this material is of key importance, as the principle of deep geological disposal
strongly relies on the sealing capacity of the host formation. The permeability being
coupled to the mechanical material state, hydromechanical coupled behaviour
of the claystone becomes important when mechanical alterations are induced by
gallery excavation in the so-called excavation damaged zone (EDZ).
In materials with microstructure such as the Callovo-Oxfordian claystone
[Robinet et al., 2012], the macroscopic behaviour has its origin in the interaction
of its micromechanical constituents. In addition to the coupling between
hydraulic and mechanical behaviour, a coupling between the micro (material
microstructure) and macro scale will be made. By means of the development
of a framework of computational homogenization for hydromechanical coupling,
a doublescale modelling approach is formulated, for which the macroscale constitutive
relations are derived from the microscale by homogenization.
An existing model for the modelling of hydromechanical coupling based on the
distinct de nition of grains and intergranular pore space [Frey, 2010] is adopted
and modi ed to enable the application of rst order computational homogenization
for obtaining macroscale stress and
uid transport responses. This model
is used to constitute a periodic representative elementary volume (REV) that
allows the representation of the local macroscopic behaviour of the claystone.
As a response to deformation loading, the behaviour of the REV represents the
numerical equivalent of a constitutive relation at the macroscale.
For the required consistent tangent operators, the framework of computational
homogenization by static condensation [Kouznetsova et al., 2001] is extended to
hydromechanical coupling. The theoretical developments of this extension are
implemented in the nite element code Lagamine (Li ege) as an independent constitutive
relation. For the modelling of localization of deformation, which in classical
FE methods su ers from the well-known mesh dependency, the doublescale
approach of hydromechanical coupling is combined with a local second gradient
model [Collin et al., 2006] to control the internal length scale of localized deformation.
By accepting the periodic boundary conditions as a regularization of the
microscale deformation, the use of the multiscale model in combination with the
local second gradient model can be used for modelling localization phenomena in
HM-coupled settings with material softening.
The modelling capacities of the approach are demonstrated by means of simulations
of oedometer tests and biaxial compression tests. The approach is demonstrated
to be a powerful way to model anisotropy in the mechanical as well as
the hydraulic behaviour of the material both in the initial material state and as an e ect of hydromechanical alterations. For the application to the modelling of
Callovo-Oxfordian claystone, microstructural REVs are calibrated to geometrical
characteristics of the inclusion that form the microstructure under consideration
and to macroscale experimental results of the mechanical behaviour. The calibrated
constitutive relation is used in the simulation of gallery excavation processes.
These computations give a proof of concept of the doublescale assessment of the
hydromechanical behaviour of the excavation damaged zones around galleries in
the context of nuclear waste disposal.
